Boiler is completely dead or shows random error indications; no response to controls despite correct power supply.
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Possible Causes
How to Fix / Troubleshooting
Safety: Isolate power before removing the boiler front panel or PCB cover. Static precautions should be observed when handling PCBs.
User checks:
- Verify that the fused spur is switched on and the fuse is intact.
- Check any external controls (programmer, room thermostat) are calling for heat.
Engineer checks:
- Confirm 230 V supply at the boiler terminals and correct polarity and earth.
- Inspect the main PCB for burn marks, swollen capacitors, or water damage.
- Check all plug-in connectors to sensors, fan, pump, and burner for secure fit.
- If supply and peripherals are correct but the board does not initiate a start sequence, replace the main control PCB with the correct Grant part number.
PCB replacement should be carried out by a qualified engineer to ensure correct configuration and safe operation.
Repair Difficulty
Required Part
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